When it comes to immigration reform, conservatives can’t even agree on the facts.

As the Senate weighs the Gang of Eight’s immigration reform bill this week, Republican lawmakers and conservative interest groups are arguing over what the cost of the path to citizenship included in the lawmakers’ plan would cost taxpayers.

In the lopsided debate, the stakes are high for the Senate lawmakers, particularly for Sen. Marco Rubio of Florida who has invested considerable political capital into advancing the reform package. But they’re also high for the Heritage Foundation and DeMint, who left the Senate in part because he felt as though he could accomplish more for the conservative movement there than in government.

Heritage argued in a newly released report that the allowing 11 million undocumented immigrants a pathway to citizenship could cost $6.3 trillion. On the other side of the debate are conservative lawmakers including Sen. Jeff Flake, a member of the Gang of 8, along with other conservative organizations who argue the Heritage report didn’t take into account the economic benefits immigration reform would bring along with it.

“With this bill, it’s the gamesmanship of making it look like it doesn’t cost,” DeMint said on Monday.

Heritage unveiled its new report, co-authored by Robert Rector, who argued the net fiscal cost of providing citizenship to 11 million undocumented immigrants would be $6.3 trillion. Rector arrived at the figure by subtracting the estimated taxes paid by immigrants whose status would become legal under a pathway to citizenship from benefits and services received. The implicit political message was: Conservatives should not support a bill that amounts to amnesty.

But Heritage is taking serious criticism for its report from a wide swath of the GOP, including Grover Norquist and the CATO Institute, who pushed back with their own critiques, arguing that the Heritage report did not take the economic benefits of immigration reform into account.

Former Mississippi Gov. Haley Barbour called Heritage’s report a “political document.” Norquist’s group, Americans for Tax Reform, laid out three criticisms of the Heritage report. Rubio tweeted a link to an analysis by Douglas Holtz-Eakin, who took the new report to task.

“Imagine the confusion among thoughtful conservatives, then, when in 2007, and repackaged and rereleased today as version 2.0, a Heritage study failed to consider the implications of reform and instead looked solely at the cost of low-skilled immigrants and those effects on the government’s profitability!” he wrote.

An April ABC/Washington Post poll showed 63 percent of Americans back a program that lets undocumented immigrants pursue legal status. That’s up from 2007, when Americans were almost evently split 49 percent to 46 percent, according to the ABC/Washington Post poll. Another survey puts support for the so-called pathway higher. A poll commissioned by FWD.us, the outside group funded by Facebook founder Mark Zuckerberg found that 71 percent of voters support a pathway to citizenship.

But among conservative Republicans, Heritage's denunciation of the Gang's plan is in tune with sentiment in the House. This was a political reality Sen. Chuck Schumer recognized last week at an event held by the Christian Science Monitor. Acknowledging that it might be hard to get conservative House members on board with the Senate version of the bill, Schumer said he was pushing to get well more than 60 votes in support of comprehensive reform in the Senate.

Already, a handful of conservative House Republicans have signaled their opposition to the Senate’s legislation, and House Republican leadership, wary of this, has indicated that any Senate legislation would not be fast-tracked in the lower chamber. DeMint tapped into that sentiment, implicitly criticizing the Senate’s approach, even though the Gang argues the process has been transparent.

“We should not be dealing with such a huge issue with a few people behind closed doors,” DeMint said on Monday.

On Monday, DeMint argued that Heritage supports a more piecemeal approach to immigration reform, calling for a reevaluation of the high-tech visa program.

DeMint, at least twice on Monday, called for a “step-by-step” approach to immigration reform, a method House Judiciary Chairman Bob Goodlatte’s laid out as well. Underscoring that approach, Goodlatte told theRichmond Times-Dispatchrecently that his committee would work on a high-skilled workers bill while the Homeland Security Committee would work on border security. In case it was unclear, Goodlatte underlined the political realities facing Republican leaders in the House.

“When you pass legislation, you have to have consensus in the House, with a Republican majority,” Goodlatte told the Times-Dispatch. “I am confident that our leadership is not going to put legislation on the floor of the House that is not going to get a strong majority of Republican legislators supporting it.”